Process of producing indigo.



UNITED STATES PATENT OFFICE.

TRAUGOTT SANDMEYER, OF IBASLE, SWITZERLAND,ASSIGNOR TO JOHN R.

GEIGY & 00., OF SAME PLACE.

PROCESS OF PRODUCING INDIGO.

SPECIFICATION forming part of Letters Patent N 0. 647,280, dated April 10, 1900.

Application filed December 7, 1899. Serial No. 739,507. (No Specimens.)

To all whom it may concern.-

Be itknown that I, TRAUGOTT SANDMEYER, a citizen of the Swiss Confederation, residing at Basic, Switzerland, have invented certain new and useful Improvements in Processes of Making Indigo, Pure and Mixed with Indigo- Red, of which the following is a specification.

Ad. Von Baeyer has proved in his fundamental works on indigo that certain derivatives of isatin-as, for instance, isatin chlorid, the pseudoisatin -alpha-oxim, and the ethers of isatin-by moderate reduction can be transformed, particularly with ammonium sulfid, into indigo, with which, however, always more or less indigo-red is formed, (Berichte den Deu/tschen Ohemischen Gescllschctfz, Vol. XI, p. 1217; XII, 4:56; XVI, 2203.)

In my application, Serial No. 739,508, filed December 7, 1899, I have described the production of a new derivative of isatin-namely, alpha-isatin-anilidof the formula:

i beta/ 3 :0

or in the tautomeric pseudoform NH \alpha o=Nc,H, beta/ rivatives, but in practical working with the very important difference that the formation of indigo from the pure substance takes place very easily and nearly without any admixture of indigo-red. However, such an admixture of indigo-red can be brought about in every desirable proportion if the reduction of the alpha-isatin-anilid is carried out in the presence of certain quantities of isatin. The ammonium sulfid which Ad. vou Baeyer has employed with success has also proved to be in this case the most suitable reducing agent.

The following examples will serve to illus trate the manner in which the invention can be carried into practical eifect. The parts are by weight:

Earctmple IProcluczion of indzIgo.To a warm solution of twenty parts of alpha-isatinanilid in sixty parts of alcohol are quickly added, with stirring, forty parts of a freshlyprepared solution of ammonium sulfid c011- taining ten per cent. of sulfureted hydrogen. By the chemical heat of the reaction the so lution turns in color to green and then to blue,

and the immediate separation of indigo inv small crystals takes place. Finally, the mix ture is boiled for a short time, and then the indigo is filtered off, Washed with hot alcohol, and dried. The sulfur it contains can be removed by treatment with carbon disulfid.

Eacctmple II-Producti0n of determinate mixtures of indigo and ind1Yqo-red.To' a warm solution of five parts of isatin and fifteen parts of alpha-isatin-anilid in sixty parts of alcohol are quickly added, with stirring, forty parts of the above (example I) mentioned solution of ammonium sulfid. The separation of the mixture of indigo with indigo-red takes place in the same way, and the further treatment is the same as that above described, Example I. In appearance the product differs little from the foregoing one. Both are dark crystalline powders showing a slight copper-colored luster; but their dyeings, also the solution of their sulfonic acids, show a surprising difference in the shades, which, according to the employed quantity of isatin,

vary from the greenish blue of pure indigo earmine to reddish violet.

In these examples the alcohol may be substituted by Water, benzol, 8m. 5 What I claim as new, and desire to secure by Letters Patent, is-

The herein-described process of producing v indigo pure and mixed with indigo-red, which consists in forming a suitable solution of alpha-isatin-anilid of the formula:

01- in the tautomeric pseudoform In testimony that I claim the foregoing as my invention I have signed my name in presence of two subscribing witnesses.

TRAUGOTT SANDMEYER.

Witnesses:

GEORGE GIFEoRD, ALBERT GRAETER. 

